Reduce journal log flood in headless mode

[kajusnau]

Description of changes

1. Prevent ghaf-launcher and eww services from starting in headless mode:
   • Added an ExecCondition check using wlr-randr to detect headless mode.
   • If headless mode is detected, the service is not started (skipped quietly), preventing repeated restart attempts from filling the logs.
   • Added explicit starting and stopping of ghaf-launcher and ewwbar services in the display-event-trigger script.
     • display-event-trigger is run every time a display change event is detected.

Addresses SSRCSP-6193

Checklist for things done

• Summary of the proposed changes in the PR description
• More detailed description in the commit message(s)
• Commits are squashed into relevant entities - avoid a lot of minimal dev time commits in the PR
• Contribution guidelines followed
• Ghaf documentation updated with the commit - https://tiiuae.github.io/ghaf/
• PR linked to architecture documentation and requirement(s) (ticket id)
• Test procedure described (or includes tests). Select one or more:
  • Tested on Lenovo X1 x86_64
  • Tested on Jetson Orin NX or AGX aarch64
  • Tested on Polarfire riscv64
• Author has run make-checks and it passes
• All automatic Github Action checks pass - see actions
• Author has added reviewers and removed PR draft status
• Change requires full re-installation
• Change can be updated with nixos-rebuild ... switch

Instructions for Testing

• List all targets that this applies to:
• Is this a new feature
  • List the test steps to verify:
• If it is an improvement how does it impact existing functionality?

[milva-unikie]

This significantly reduced the log size of Orin-NX in test-automation.

• Cross-compiled Orin-NX: 13M -> 153K
• Native Orin-NX: 4.7M -> 50K

(Failed NUC test in pre-merge-pipeline is most likely unrelated to this PR. Edit. Confirmed manually that it works, something just went wrong in pre-merge-pipeline)